The invention relates to a semiconductor device for determining or controlling the position of a radiation beam. The beam is incident upon a major surface of radiation-sensitive semiconductor body provided with at least two radiation-sensitive diodes which form a rectifying junction with an adjacent part of the semiconductor body. The diodes provided with electrical connections to drain away electric current produced by the incident radiation.
The position of the radiation beam is to be understood to mean the position of the balance of the beam. As usual, the term balance is to be understood to mean the point at which the number of photons incident per unit time is the same on either side of this point. With symmetrical beams this point coincides with the axis of the beam.
Radiation-sensitive semiconductor devices of the aforementioned kind are used, for example, in photosensitive circuit arrangements for picture display and in arrangements for tracking or positioning light beams (or beams of radiation of other kinds). Other applications of radiation detection are in the field of spectroscopic analysis, especially in the wavelength range of from 200 to 1100 nm, and, for example, soft X-ray radiation. Such arrangements are also used for detection of particle radiation (for example electrons, .alpha. particles or high-energetic particles). Such semiconductor devices (especially in the wavelength range of visible light) are also used in measuring apparatus for position determination, for example for measuring a bend, or, for example, in automatic assembly lines.
The invention further relates to a focus error detection system provided with a semiconductor device according to the invention and to an arrangement for reading and writing information in a radiation-recording surface of a record carrier, which arrangement is provided with such a focus error detection system.
A semiconductor device of the kind mentioned in the opening paragraph is described in the Netherlands Patent Application No. 8003906 of the Applicant laid open to public inspection on Feb. 1.sup.st 1982. This Application describes a focus error detection system for detecting a deviation between a first radiation-reflecting surface and a second focusing surface of an objective system (for example for a compact disk or video disk arrangement), in which a so-called quadrant diode is utilized.
The quadrant diode described therein acts very rapidly, indeed, and has a transition curve of high steepness. But during mounting, the diode has to be mounted so that with correct focusing the radiation beam strikes the semiconductor surface exactly between the four quadrants of the diode. In view of the tolerances then required (the relative distance of the quadrants is approximately 5 .mu.m), such a mounting process with associated adjustment is difficult and time-consuming.
Similar mounting problem arise in a focus error detection system in which a beam splitting element followed by a radiation-sensitive detection system comprising a plurality of detectors separated from each other by narrow strips is arranged in the path of the beam reflected by the radiation-reflecting surface, the subbeams formed by the beam-splitting element being incident upon the separation strips. In the latter case, it can be ensured that the centres of the radiation spots formed by the subbeams in the detector surface are incident upon the separation strips with a correct focusing by causing the separation strips to enclose an acute angle with each other. By means of a mechanical displacement of the detector surface, a correct initial adjustment can then be obtained, as is described more fully in Netherlands Patent Application No. 8202058 of the Applicant. This mechanical adjustment may vary with time and/or with temperature, however, after which a new and often labarious adjustment of the detector plane is necessary.